Comparative study of cytoplasmic elimination in spermatids of selected mammalian species

In the transformation of a spermatid into a spermatozoon, cytoplasmic loss occurs, allowing the sperm to swim unhindered. Cytoplasmic loss takes place via elimination of the residual body and through structures known as tubulobulbar complexes. A determination of cytoplasmic loss in several species was undertaken by using high-resolution electron microscopic morphometric techniques. During the period that tubulobulbar complexes are present, an average 53% cytoplasmic loss was recorded for five species (guinea pig, 48.8 +/- 6.2% (SEM); monkey, 60.3 +/- 4.3%; opossum, 54.5 +/- 4.4%; rabbit, 46.9 +/- 2.7%; and rat, 55.7 +/- 4.9%), whereas there was essentially no loss or gain in cytoplasm during the same period for round spermatids. Surprisingly, during spermatid elongation an approximate 36% loss of cytoplasm was also recorded for five species (guinea pig, 50.1 +/- 6.3%; monkey, 30.0 +/- 15.4%; opossum, 25.4 +/- 9.0%; rabbit, 42.4 +/- 8.6%; and rat, 34.9 +/- 11.9%), which is only partially (approximately 60%) accounted for by fluid pumping from the nucleus during nuclear condensation. A densification of the cytoplasm of elongate spermatids, as compared with round spermatids, suggests fluid is also pumped from the elongating spermatid cytoplasm. Fluid loss from germ cells may contribute to the seminiferous tubule fluid, a fluid previously thought to be solely of Sertoli-cell origin.     

Immunohistochemical localization of a water channel, aquaporin 7 (AQP7), in the rat testis

Cell volume reduction is one of the most distinct morphological changes during spermiogenesis and may be largely attributable to water efflux from the cell. A strong candidate for a water efflux route, aquaporin 7 (AQP7), which is a water channel, was studied immunohistochemically in the rat testis. Immunoreactivity was restricted within the elongated spermatids, testicular spermatozoa, and residual bodies remaining in the seminiferous epithelium. Weak but distinct immunoreactivity was first observed in the cytoplasmic mass of the spermatid at step 8 of spermiogenesis. The Golgi-like apparatus became steadily immunoreactive at step 10. The plasma membrane covering the cytoplasmic mass showed strong immunoreactivity after step 16. At this step, the middle piece of the tail also showed immunoreactivity at the portion protruding into the lumen. The whole head and distal tail, where the elongated spermatid had only a limited amount of cytoplasm, showed no immunoreactivity throughout spermiogenesis. After spermiation, the immunoreactivity of AQP7 remained at the middle piece and in the cytoplasmic droplet in the testicular spermatozoon. The present observations suggest that AQP7 contributes to the volume reduction of spermatids, since this water channel protein is localized on the plasma membrane covering the condensing cytoplasmic mass of the elongated spermatid, and since the seminiferous tubule fluid is hypertonic.     

The role of sertoli cells in spermatid maturation in the testis of the crayfish, Procambarus paeninsulanus

With the onset of spermiogenesis, many changes become apparent in the crayfish spermatid during its transition to mature sperm. The nucleus passes through a series of stages, excess cytoplasm is removed, the acrosome develops, and nuclear arms form and become wrapped around the sperm prior to its enclosure in a capsule. Changes are also apparent in the Sertoli cells surrounding the germ cells in the crayfish testis. The amount of cytoplasm of individual Sertoli cells appears to increase in quantity and changes in the intracellular organelles become apparent. As spermiogenesis commences, the cytoplasm along one side of Sertoli cells adjacent to the spermatids is devoid of obvious organelles. Numerous finger/like projections of Sertoli cytoplasm penetrate into the spermatid and appear to isolate portions of the sperm cytoplasm. During later stages of spermiogenesis, several vesicles in the Sertoli cells which appear to contain droplets of this isolated sperm cytoplasm. appear to undergo lytic changes, As the amount of cytoplasm of the spermatid is reduced, contact is maintained between the spermatid and Sertoli cell in the area of the acrosome. The nuclear arms of the sperm extend into the Sertoli cell during their formation and later become wrapped around the acrosomal area of the sperm. At this time, very little space exists between the Sertoli cell and its many sperm. Large vesicles of electron dense material appear to be released by the Sertoli cells into the space between the sperm and Sertoli cell. This material completely surrounds the sperm and forms the sperm capsule. Spermiation involves the gradual dissolution of the points of contact between the sperm capsule and the Sertoli cell.     

Spermiogenesis in the bluegill (Lepomis macrochirus): a study of cytoplasmic events including cell volume changes and cytoplasmic elimination

The process involved in the reduction of both nuclear and cytoplasmic volume was investigated in the bluegill (Lepomis macrochirus), a teleost fish. Young spermatids contained centrally positioned nuclei which, with time, moved toward the cell surface to become eccentrically positioned. Chromatin condensation was initiated from a region near the implantation fossa, whereas at the opposite pole of the nucleus an area sparse in heterochromatin (clear area) was noted. The nuclear membrane lying adjacent to the clear area dissolved and subsequently reformed, yielding a nucleus with a reduced volume. During this process, packets of cytoplasm surrounded by a double membrane were formed along the future midpiece. The packets of cytoplasm migrated toward the cell surface, protruded from the surface, and were extruded into the spermatocyst lumen. These structures, termed residual bodies, were subsequently endocytosed, accumulated into large phagocytic vacuoles, and eventually degraded by the nearby Sertoli cell. When the spermatocyst ruptured, spermatozoa containing sparse cytoplasm were released into the excurrent duct system. During spermiogenesis, both the nuclear and cytoplasmic volumes decreased substantially (80%, 92% respectively) leading to an overall 87% reduction in total cell volume.     

Fine structural changes in Sertoli and Leydig cells during the reproductive cycle of the ground squirrel, Citellus lateralis

During spermatogenesis in sexually mature ground squirrels Leydig and Sertoli cells were morphologically well differentiated. For Leydig cells the most prominent organelles were lipid droplets, mitochondria with tubulo-vesicular cristae and abundant agranular reticulum organized as a mass of anastomosing tubules. These morphological criteria suggest that the Leydig cells were steroidogenically active. Sertoli cells exhibited a topographical distribution of certain organelles with basal regions containing stacks of granular reticulum, and large areas of agranular reticulum. The cytoplasm surrounding maturing germ cells contained numerous microtubules, and an adluminal layer of spermatids at a certain stage of spermiogenesis became enveloped by Sertoli cytoplasm containing an enormous proliferation of agranular reticulum. The presence of these organelles in Sertoli cells suggests that during spermatogenesis they are active in the synthesis of proteins and steroids. In particular the mass of agranular reticulum surrounding late stage spermatids indicates that steroids may be required for spermatid maturation and/or spermiation. By contrast Leydig and Sertoli cells observed during testicular regression, when only spermatogonia remain in the seminiferous tubules, had undergone structural changes. Leydig cells were still numerous and large with abundant agranular reticulum that was now organized as a loose assemblage of single unbranched tubules. Sertoli cells were drastically reduced in both cytoplasmic volume and content of organelles.     

Cytoskeletal involvement in spermiation and sperm transport

The process of spermiation and sperm transport was studied using specific inhibitors of cytoskeletal elements. Within 12-24 hr after the intratesticular injection of taxol, a compound that acts to stabilize microtubules and inhibit microtubule-related processes, an unusually large number of microtubules was seen within the body of the Sertoli cell. At the same time, transport of elements within the seminiferous epithelium was affected. At the end of stage VI of the cycle, step 19 spermatids were maintained in the deep recesses of the Sertoli cell and not transported to the rim of the seminiferous tubule lumen. At stage VIII, residual bodies remained at, or near, the rim of the tubule and were not transported to the base of the tubule. They underwent only partial degradation at this site, indicating that there may have been two phases involved in their dissolution--one autophagic and one phagocytic, but the latter did not occur since the residual bodies were not transported to Sertoli lysosomes at the base of the tubule. The observations suggest that microtubules are involved in transport processes within the seminiferous epithelium. Within 1-12 hr after the intratesticular injection of 500 microM cytochalasin D, a compound which interferes with actin-related processes, normal appearing tubulobulbar complexes were not present. The tubular portion (distal tube) of the complex did not initiate development. It was assumed that filaments (which were identified as such using NBD-phallacidin and the S-1 fragment of myosin) played an important role in the development of this portion of the complex. Cells did not eliminate cytoplasm normally, as evidenced by an enlarged cytoplasmic droplet, further emphasizing the published role for tubulobulbar complexes in cytoplasmic elimination. Although sperm were released normally from stage VIII tubules, many remained within the tubular lumen and did not traverse the duct system. Cytochalasin did not inhibit fluid secretion by the Sertoli cell, as demonstrated by efferent duct ligation, but did alter myoid cell actin cytoskeletal organization, suggesting that myoid cell contractility is primarily responsible for transport of sperm. Overall, the observations suggest that cytoskeletal activity of the Sertoli cell is important for several aspects of the spermiation process as well as sperm transport.     

Rat testis motor proteins associated with spermatid translocation (dynein) and spermatid flagella (kinesin-II)

In this study, we report sites in the seminiferous epithelium of the rat testis that are immunoreactive with antibodies to the intermediate chain of cytoplasmic dynein and kinesin II. The study was done to determine whether or not microtubule-dependent motor proteins are present in Sertoli cell regions involved with spermatid translocation. Sections and epithelial fragments of perfusion-fixed rat testis were probed with an antibody (clone 74.1) to the intermediate chain of cytoplasmic dynein (IC74) and to kinesin-II. Labeling with the antibody to cytoplasmic dynein was dramatically evident in Sertoli cell regions surrounding apical crypts containing attached spermatids and known to contain unique intercellular attachment plaques. The antibody to kinesin II reacted only with spermatid tails. The levels of cytoplasmic dynein visible on immunoblots of supernatants collected from spermatid/junction complexes treated with an actin-severing enzyme (gelsolin) were greater than those of controls, indicating that at least some of the dynein may have been associated with Sertoli cell junction plaques attached to spermatids. Results are consistent with the conclusion that an isoform of cytoplasmic dynein may be responsible for the apical translocation of elongate spermatids that occurs before sperm release. Also, this is the first report of kinesin-II in mammalian spermatid tails.     

Observations of spermiogenesis and epididymal sperm maturation in the rufous hare wallaby, Lagorchestes hirsutus (Metatheria, Mammalia)

Acrosomal development in the early spermatid of the rufous hare wallaby shows evidence of formation of an acrosomal granule, similar to that found in eutherian mammals, the Phascolarctidae and Vombatidae. Unlike the other members of the Macropodidae so far examined, the acrosome of this species appears to be fully compacted at spermiation and extends evenly over 90% of the dorsal aspect of the nucleus. During spermiogenesis, the nucleus of the rufous hare wallaby spermatid showed evidence of uneven condensation of chromatin; this may also be related to the appearance of unusual nucleoplasm evaginations from the surface of the fully condensed spermatid. This study was unable to find evidence of the presence of Sertoli cell spurs or nuclear rotation during spermiogenesis in the rufous hare wallaby. The majority of spermatozoa immediately before spermiation had a nucleus that was essentially perpendicular to the long axis of the sperm tail. Nuclei of spermatozoa found in the process of being released or isolated in the lumen of the seminiferous tubule were rotated almost parallel to the long axis of the flagellum; complete parallel alignment occurred during epididymal maturation. At spermiation spermatozoa have characteristically small cytoplasmic remnants compared to those of other macropods. Unlike the majority of macropodid spermatozoa so far described, the spermatozoa of the rufous hare wallaby showed little evidence of morphological change during epididymal transit. There was no formation of a fibre network around the midpiece or of plasma membrane specializations in this region; the only notable change was a distinctive flattening of midpiece mitochondria and scalloping of the anterior mitochondrial sheath to accommodate the sperm head. Preliminary evidence from spermiogenesis and epididymal sperm maturation supports the classification of the rufous hare wallaby as a separate genus but also indicates that its higher taxonomic position may need to be re‐evaluated.     

Studies on the polymorphic spermatozoa of a marine snail. 2. Genesis of the eupyrene sperm

Spermiogenesis of the eupyrene sperm in the snail, Fusitriton oregonensis, was studied with light and electron microscopes. Endoplasmic reticulum, which encircles the nucleus in each spermatid, appears to connect with the Golgi body and to interconnect between adjacent spermatids via cytoplasmic bridges. It is suggested that as the Golgi body migrates around the nucleus the endoplasmic reticulum may circulate with it. The alignment of the proacrosome with the nucleus is effected by a 180° rotation of the Golgi body, after which it separates and migrates posteriorly with the residual cytoplasm. Each sperm possesses a well-developed intracellular digestive system as indicated by multivesicular bodies, residual bodies, and myeloid figures. Autophagy begins in the residual cytoplasm before it is released from the middle piece. Microtubules are found outside the nucleus and mitochondria during the final stages of spermiogenesis, when elongation is almost complete. These microtubules appear to be involved in the final shaping and twisting process, in which torsion is locked in the nucleus and the mitochondria spiral around the axoneme. The annulus attaches the distal centriole to the plasma membrane in the early spermatid and as flagellar production begins they move towards the implantation fossa at the base of the nucleus. There are two centrioles in the early spermatid, the distal centriole and procentriole. The small procentriole fuses with the distal centriole in the intranuclear canal to form the centriolar cap of the basal body. This cap is pushed through the end of the nuclear tube and is separated from the subacrosomal space by only the nuclear membranes.     

Exposure to constant light during testis development increases daily sperm production in adult Wistar rats.

Testis histometry and daily sperm production (DSP) were evaluated in adult (160-day-old) Wistar rats exposed to constant light for the first 25 days after birth, and compared with control animals which were exposed to a 12 h-light-12 h-dark light regimen. Significantly greater (P < 0.05) numbers of Sertoli cell nucleoli and round spermatids per cross-section of seminiferous tubule were found in animals exposed to constant light. In addition, epididymis weight, DSP per testis and per gram of testis, as well as Leydig cell compartment volume, were significantly increased in treated animals. Although there was a clear trend toward an increased Sertoli cell population per testis in animals exposed to constant light, this difference was not statistically significant (P < 0.05). The number of round spermatids as expressed per Sertoli cell was the same in both groups. Surprisingly, the diameter and volume of round spermatid nucleus at stages I and VII of the cycle of seminiferous epithelium were significantly lower (P < 0.05) in treated animals. In conclusion, constant illumination during neonatal testis development increased sperm production and Leydig cell compartment volume in adult rats probably through a mechanism involving elevated follicle stimulating hormone and luteinizing hormone during the prepubertal period. To our knowledge, this is the first study showing that altering the light regimen can affect sperm production in non-seasonal breeders.     

Diversity of Sertoli cells in the testis of Saduria entomon L. (Crustacea,Isopoda)

Summary

The present paper is the first to give a comprehensive and detailed characterization of Sertoli cells in the isopod, Saduria entomon, based on transmission electron microscopy. Two types of Sertoli cells, A and B, were distinguished which clearly differ in their location in the wall of the testicular tubule, and in their morphology, ultrastructure, and function. Their occurrence is closely connected with the characteristic arrangement of germ cells inside the tubule. Sertoli A cells occupy only the part of the tubule containing spermatogonia and primary spermatocytes and they are associated with these cells by means of numerous ramified processes running in many directions. They are irregular in shape, but their shape and the ultrastructure are stable during maturation of the germ cells. Sertoli B cells, which compose most of the testicular tubule wall, form a columnar epithelium. They send long processes into the lumen of the tubule by means of which they make contact with maturing spermatids. The cytoarchitecture of the processes is highly variable and reflects their role in spermiogenesis and the formation of sperm bundles. After spermiation, when the apical part of the Sertoli cells has become flattened, they phagocytoze the residual cytoplasmic masses of spermatids, which undergo degradation in heterophagic vacuoles. Simultaneously, numerous autophagic vesicles appear.     

Testicular expression of small ubiquitin-related modifier-1 (SUMO-1) supports multiple roles in spermatogenesis: silencing of sex chromosomes in spermatocytes, spermatid microtubule nucleation, and nuclear reshaping

SUMO-1 is a member of a ubiquitin-related family of proteins that mediates important post-translational effects affecting diverse physiological functions. Whereas SUMO-1 is detected in the testis, little is known about its reproductive role in males. Herein, cell-specific SUMO-1 was localized in freshly isolated, purified male germ cells and somatic cells of mouse and rat testes using Western analysis, high-resolution single-cell bioimaging, and in situ confocal microscopy of seminiferous tubules. During germ cell development, SUMO-1 was observed at low but detectable levels in the cytoplasm of spermatogonia and early spermatocytes. SUMO-1 appeared on gonosomal chromatin during zygotene when chromosome homologues pair and sex chromatin condensation is initiated. Striking SUMO-1 increases in the sex body of early-to-mid-pachytene spermatocytes correlated with timing of additional sex chromosome condensation. Before the completion of the first meiotic division, SUMO-1 disappeared from the sex body when X and Y chromosomal activity resumed. Together, these data indicate that sumoylation may be involved in non-homologous chromosomal synapsis, meiotic sex chromosome inactivation, and XY body formation. During spermiogenesis, SUMO-1 localized in chromocenters of certain round spermatids and perinuclear ring and centrosomes of elongating spermatids, data implicating SUMO-1 in the process of microtubule nucleation and nuclear reshaping. STAT-4, one potential target of sumoylation, was located along the spermatid nuclei, adjacent but not co-localized with SUMO-1. Androgen receptor-positive Leydig, Sertoli, and some peritubular myoepithelial cells express SUMO-1, findings suggesting a role in modulating steroid action. Testicular SUMO-1 expression supports its specific functions in inactivation of sex chromosomes during meiosis, spermatid microtubule nucleation, nuclear reshaping, and gene expression.     

Development of the acrosome and alignment,elongation and entrenchment of spermatids in procarbazine-treated rats

Intraperitoneally administered procarbazine caused, among other features previously reported (Russell et al., 1983), specific defects in the acrosome of cap phase spermatids of the rat seminiferous epithelium. The effect of procarbazine was to fragment and eventually cause resorption of the acrosomes of a small number of steps 5–9 spermatids. Although the acrosome was lost, dose union of the leaflets of the nuclear envelope underlying the acrosomal sac was maintained as was the marginal fossa and acrosomal zonule. Spermatids at steps 8 and 9 of development, which had lost their acrosomes, showed nuclei which were eccentric within the cell—a feature which normally occurs at these steps of spermiogenesis in acrosome intact cells. Even without an acrosomal sac, the plasma membrane of these cells (in stage VIII) became orientated to the region of the nuclear membrane which would have underlaid the acrosome. Although abundant, Sertoli ectoplasmic specialization did not become aligned with the spermatid head. The spermatid failed to become orientated within the seminiferous epithelium and failed to enter the crypts within the Sertoli cell as usually occurs during the elongation process. Thus, the presence of an acrosome is not likely related to the formation of an eccentric nucleus or the alignment of the surface of the nucleus which would normally underlay the acrosome with the cell's plasma membrane (internal alignment). The presence of an acrosome may be related to the alignment of the spermatid head with the ectoplasmic specialization, which in turn may influence the orientation and positioning of the late spermatids within the seminiferous epithelium (external alignment) and their position within recesses of the Sertoli cell. This study also suggests a role for the manchette in the process of elongation of the spermatid.     

Developmental expression of spermatid-specific thioredoxin-1 protein: transient association to the longitudinal columns of the fibrous sheath during sperm tail formation

The mammalian sperm tail presents a complex organization in which a number of additional structures, namely outer dense fibers and fibrous sheath, surround the central axoneme and are thought to regulate flagellar motility. We have previously described a novel member of the thioredoxin family of proteins with a spermatid specific expression pattern, spermatid-specific thioredoxin-1 (Sptrx-1). We report here the developmental analysis of Sptrx-1 expression during murine spermiogenesis. Immunocytochemical analysis of Sptrx-1 through the different steps of spermiogenesis in rat seminiferous tubule sections showed that its expression begins at step 9, gets progressively stronger until steps 14-16 (where a peak is reached), and then diminishes in steps 17 and 18 until practically no immunolabeling is detected in step 19 spermatid. During its transient expression in spermiogenesis, Sptrx-1 is most concentrated in the periaxonemal compartment of the tail of the elongating spermatid, except in the very last steps (steps 17-19), when periaxonemal labeling disappears and a residual buildup of Sptrx-1 occurs in the shrinking cytoplasmic lobe. Electron microscopic analysis by immunogold labeling pinpointed the localization of Sptrx-1 to the assembling longitudinal columns of the fibrous sheath, whereas the forming ribs of the fibrous sheath were unlabeled. Immunoblotting of isolated fibrous sheath and tails obtained from epididymal or ejaculated sperm of rat and human confirmed our immunocytochemical observation: Sptrx-1 is no longer a component of the mature fibrous sheath. To our knowledge, this is the first report of a protein that specifically associates to the fibrous sheath during development but does not become a permanent structural component. The expression pattern of Sptrx-1 during rat spermiogenesis suggests that it could be part of a nucleation center for the formation of the longitudinal columns and transverse ribs that bridge the latter.     

Morphological changes in the rat sertoli cell induced by the microtubule poison carbendazim

Early morphological changes in the rat Sertoli cell induced by the fungicide carbendazim (methyl-2-benzimidazole carbamate; MBC), a metabolite of benomyl, were examined. Adult rats were treated with single doses of MBC (400mg/kg) or vehicle and examined by light and electron microscopy at 3 hr post-treatment. Sloughing of elongating spermatid clusters was observed in all stages of spermatogenesis, except for Stages III–V. Cleavage occurred near the apical region of the seminiferous epithelium where cytoplasmic processes of the Sertoli cell surround the heads of elongating spermatids. The cleaved cytoplasm remained attached to the sloughed spermatids and ectoplasmic specializations remained undamaged. Intact microtubules were observed in the apical Sertoli cell cytoplasm (including sloughed tissues) but were decreased in the body region, where aggregates of mitochondria were found. Cytoplasm near the cleavage site exhibited rarefaction, which was associated with swollen cisternae of endoplasmic reticulum. It appears that the mechanism of germ cell sloughing induced by MBC treatment involves the disruption of microtubules in the body region of the Sertoli cell, the retraction of cytoplasmic organelles and the swelling of endoplasmic reticulum.     

La spermatide, cette méconnue

The use of microinsemination of round or elongated spermatids into ovocytes, in certain cases of male infertility, requires re-examination of the sequence of morphological and functional changes that occur throughout spermiogenesis. This paper reviews essential findings on morphogenesis of spermatids, genome expression during sperm differentiation and cellular interactions between spermatids themselves and between spermatids and Sertoli cells. Round and elongated spermatids appear to represent two classes of structuraly and functionnaly different cells. One question remains: on what criteria can one claim that a round spermatid functions normally when spermiogenesis is blocked or impaired?     

粗糙沼虾精巢发育的组织学

利用光镜技术,对粗糙沼虾精巢发育进行了研究,根据精子发生过程中每种生殖细胞所占的比例和发生的次序,并结合精巢的形态特征,把精巢发育过程分为五个时期,即精原细胞期,精母细胞期,精细胞期,成熟精子期及退化期,精原细胞期,精巢小,透明乳白色,生精小管内的生殖细胞以精原细胞为主;精母细胞期;精巢体积增大,半透明乳白色,主要由处于初级精母细胞的次级精母细胞阶段的生殖细胞组成;精细胞期,精巢体积继续增大,颜色加深,生精小管内的生殖细胞以精细胞为主;成熟精子期,精巢体积可达最大,紫红色,生精小管内充满着成熟的精子,退化期;精巢体积减小,半透明乳白色,生精小管内的成熟精子几乎排空。     

Spermiation in the Mouse: Contribution of the Invading Sertoli Cell Process to Adluminal Displacement of the Spermatid Head

At the maturation phase of spermiogenesis in mice, the spermatid heads that are embedded deeply in the epithelium of the seminiferous tubules dislocate toward the luminal surface. In the present study, to clarify the manner in which the spermatid head is displaced toward the lumen, morphological changes in spermatids and Sertoli cells were examined on ultrathin and thick sections stained with adenosine triphosphatase cytochemistry. During adluminal displacement, the spermatid head is surrounded by an invading process of Sertoli cell which invaginates into the spermatid cytoplasm to form complicated passages called the canal complex. At the site of the spermatid head, the wall of an invading Sertoli cell process folds to form a sheath in which the spermatid head is located. The sheath correspond to a structure known as ectoplasmic specialization. The invading Sertoli cell process also shows branching and swelling at the site where spermatid heads are present. The present results suggest that the canal complex is directly involved in the adluminal displacement of the spermatid head. Dynamic changes of invading Sertoli cell processes may produce the motive force for adluminal displacment of the spermatid head. Also, ectoplasmic specialization may contribute to the adluminal displacement of the spermatid possibly by mediating cell to cell interaction between the spermatid nucleus and the invading Sertoli cell process.     

Fine structural observations on the process of spermiation in the holocephalan fish Hydrolagus colliei

The process of spermiation in the ratfish Hydrolagus colliei is described and compared with that in mammals and amphibians. Spermiation in this species involves prior fluid space expansion both within the apical parts of the Sertoli cytoplasm and in the spaces between Sertoli cells and spermatids. The apical ends of Sertoli cells fragment, including the parts immediately around the spermatid acrosomes. Intercellular material between the spermatid tips and the Sertoli cells dissolves. Concurrently an opening from the seminiferous follicle into the efferent ductule is made by means of changes in cell shape and separation of Sertoli cells and efferent ductule cells that adhere to each other up to the time of sperm release.